This invention concerns a wooden beam used extensively, especially when in the form of lattice beams, as sheathing in poured-concrete construction. More specifically it concerns wooden beams with elements that consist of large-surfaced sheathing panels the backs of which are strengthened with several parallel steel flanges and to which a large number of parallel wooden lattice beams are anchored to provide the panels with the requisite stiffness. These large-surfaced sheathing elements are light in weight and easy to nail and clean. Problems arise however from the necessity of having sheathing panels of various size available. This demand is encountered especially with wall sheathing because contemporary construction often calls for stories of different height, which requires changing the height of the sheathing. To satisfy this requirement for sheathing elements of different height, the wooden lattice beams that are used with them are delivered in different lengths, for example, in ten different lengths ranging from 2.56 to 6 m. This means that a large assortment of beams must be kept in stock for the appropriate length to be readily available.
To decrease the number of various beam lengths that must be kept in stock, adjustable beams are known. German Patent No. 1 147 018 discloses one example. The length of the sheathing beams specified in that document are adjustable and consist of two wooden lattice beams that slide together inside bands that can be braced against the beams with wedges. These beams have proved to be excellent, although they have the drawback of overlapping, which adds the thickness of one beam (approximately 10 cm) at the point of overlap and makes the surface to be sheathed uneven.
Joining beams of various lengths together, especially into overlength beams of 10 to 15 m, with dovetail joints is also known. These overlength beams are intended to be taken apart at the joint later by the customer when shorter beams are required. In practice, however, they are usually not taken apart but are kept unseparated at the yard, which complicates the storage problem.